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Old 11-17-2011, 12:33 PM   #1
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Wire gauge for water heater and rewiring


First, I know nothing about wiring or anything and have no plans to do any myself. I just need to know where to start.

I live in a mobile home and have a MH specific water heater. It's a single element heater 4500 Watts and run on 240.

The heater has started leaking and I have to replace it. The problem is that just about the only thing I can find are dual element heaters and from what I'm reading in the instruction manuals, 10 gauge wiring is called for.

My current 4500 Watt/240 Volt heater is being supplied by 12/2 wire.

First, why would there be a difference in wiring between my old heater and a new one if the old one has been supplied with a 12/2 line for 10 years?

Second, both my water heater and furnace on are double throw thirty amp breakers. Is a dual element heater going to make any kind of difference where something in the panel would need to be changed.

Finally, having used the 12/2 wire for 10 years, does it need to be rewired with 10 gauge for a new heater?

Thanks for any help you can provide.

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Old 11-17-2011, 01:28 PM   #2
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Wire gauge for water heater and rewiring


The reason it is calling for 10awg wire is that a heater of that size pulls more than 18 amps. (not by much) code limits 12awg to 18amps. So legally you do need to upgrade the wiring.

Nothing should change in the panel.

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Old 11-17-2011, 01:41 PM   #3
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The reason it is calling for 10awg wire is that a heater of that size pulls more than 18 amps. (not by much) code limits 12awg to 18amps.
What???

The reasons is that a storage type water heater must be considered a continuous load. So a 20A circuit with a continuous load is limited to 16A.

A 20A circuit without a continuous load is limited to 20A.
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Old 11-17-2011, 02:54 PM   #4
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Wire gauge for water heater and rewiring


I appreciate the responses, but I'm a little confused.

The water heater I'm purchasing is rated at 18.8 amps. The wiring that came with the home for the water heater is 12/2 and that old water heater was 4500 watts just like the one I'm getting. I've got a 30 Amp breaker.

Will something happen to the wiring if I put the new water heater on the existing 12/2?
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Old 11-17-2011, 03:27 PM   #5
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You should NOT have a 30A breaker for 12/2 wire. As previously noted, 12 gage wire is limited to a maximum of 20A for intermittent use, and 16A for continuous use. That means that 12/2 wire must be on a 20A or smaller breaker.

When you upgrade the wiring to 10 gage, then you can have a 30A breaker on the circuit. So you can keep your 30A breaker so long as you replace the 12 gage wire with 10 gage wire.
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Old 11-17-2011, 03:41 PM   #6
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You should NOT have a 30A breaker for 12/2 wire. As previously noted, 12 gage wire is limited to a maximum of 20A for intermittent use, and 16A for continuous use. That means that 12/2 wire must be on a 20A or smaller breaker.

When you upgrade the wiring to 10 gage, then you can have a 30A breaker on the circuit. So you can keep your 30A breaker so long as you replace the 12 gage wire with 10 gage wire.
Okay, as I mentioned, I know nothing about this stuff. I went back to the box and figured out what was going on with where the breakers are located. The water heater breakers are actually 20 Amps. They're arranged around other breakers like this:

20A
30A
30A
20A

So, that means I've got the right breaker for the size wiring.

That said, can I use the existing wiring for the new water heater that's rated at 18.8 Amps? It's a 4500 Watt water heater, dual elements, and 240 volts.

Again, I appreciate the input.
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Old 11-17-2011, 04:05 PM   #7
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What???
A 20A circuit without a continuous load is limited to 20A.
Have you read the fine print notes on the table that you glanced at?
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Old 11-17-2011, 04:06 PM   #8
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in canada you could use a 25A breaker on a 12g wire for heaters only up to 4800w load, but i dont think same rule apply in the nec. Anyway there is nothing dangerous leaving 20A breaker and 12g, worse that can happen is that breaker could trip after 3-4 hour of continuous water heating (that will never happen anyway)
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Old 11-17-2011, 04:35 PM   #9
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Have you read the fine print notes on the table that you glanced at?
What table are you talking about?

A 20 amp breaker is fine for 20 amps non-continuous.
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Old 11-17-2011, 06:20 PM   #10
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Have you read the fine print notes on the table that you glanced at?
Glanced at? Ok.

I'm sure I have. Which in particular are you talking about?
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Old 11-17-2011, 06:42 PM   #11
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Sounds like there is an echo in here.
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Old 11-17-2011, 07:54 PM   #12
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did you check the www.Grainger.com catalog they have low,compacts listed with single 240V elements models #3WA67 types
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Old 11-17-2011, 09:26 PM   #13
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Originally Posted by Speedy Petey View Post
Glanced at? Ok.

I'm sure I have. Which in particular are you talking about?
Who is this guy, every post I have seen of his, he is giving bad or wrong answers.
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Old 11-17-2011, 09:37 PM   #14
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sorry guys been plumbing for 30 +years here in pa never seen a electric water heater on any thing less than 30 amp 10/2 wire.....65-70 percent of fires are from faulty electric...
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Old 11-17-2011, 09:44 PM   #15
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.....65-70 percent of fires are from faulty electric...
And 75% of those are from extension cords.
They love to throw the "electrical fire" blame on almost everything.

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